Biodiesel-fischer-tropsch hydrocarbon blend

ABSTRACT

The invention provides a biodiesel and Fischer-Tropsch derived hydrocarbon blend, whereby the characteristics of the Fischer-Tropsch derived hydrocarbon are used to improve the diesel-like characteristics of biodiesel. The invention also provides a blending component for Compression Ignition engine fuel as well as a method of adjusting the density of a hydrocarbon fuel.

FIELD OF INVENTION

[0001] This invention relates to blending Fischer-Tropsch fuel withbiodiesel.

BACKGROUND OF THE INVENTION

[0002] Various companies globally are processing various agriculturallybased fatty oils to “biodiesel”, which is typically the methyl or ethylester of the respective fatty acids of the triglyceride fatty oils.

[0003] This biodiesel can be used “neat” as a diesel substitute, butmore typically is used as a blend (between 5-20%) with conventional(crude based) diesel, for example, SAE 962065.

[0004] Advantages of using biodiesel include the attractive low sulphurand low aromatics content, excellent lubricity and as a renewable fuel,the low net impact on the environment (CO₂ emissions etc) compared withfossil fuels.

[0005] The oxygen content of biodiesel is generally considered to aidsome particulate matter (PM) reduction (ref. SAE 199901-1475).

[0006] Disadvantages for biodiesel when compared to the proposed 2000World Wide Fuel Charter for diesel (Category IV) include:

[0007] Marginal cetane no. (50 vs. recommended >55)

[0008] a fuel density that exceeds the recommended density

[0009] excessive viscosity at 40° C.

[0010] a measurably lower calorific value

[0011] marginal properties for cloud point and final boiling point

[0012] Some characteristics of biodiesel are thus sub-optimal withrespect to the intentions of engine manufacturers.

[0013] Fischer-Tropsch diesel can be produced from preferably naturalgas but also other hydrocarbon feedstocks, and shares thecharacteristics with biodiesel of an environmentally friendly lowsulphur, low aromatics content fuel. Whereas biodiesel consists ofmainly linear oxygenates (esters), Fischer-Tropsch diesel consists ofmainly highly linear paraffins.

SUMMARY OF THE INVENTION

[0014] In this specification, unless the context clearly indicates thecontrary, “Biodiesel” is considered to encompass all biologicallyderived oils such as, but not limited to, rape seed, cotton, sunflower,coconut and palm, animal fats, soya, etc.; which may have been processedto methyl or ethyl esters of the triglyceride fatty oils.

[0015] According to a first aspect of the invention, there is provided abiodiesel and Fischer-Tropsch derived hydrocarbon blend, whereby thecharacteristics of the Fischer-Tropsch derived hydrocarbon are used toimprove the “diesel” characteristics of biodiesel, for example, fattymethyl esters.

[0016] The Fischer-Tropsch derived hydrocarbon may be blended withbiodiesel in varying ratios to improve the resultant diesel fuel'scharacteristics.

[0017] Thus the invention provides a hydrocarbon composition for use incompression ignition engines (CI), said composition comprising a blendof Fischer-Tropsch derived hydrocarbon and biodiesel in a volumetricratio of from 1:5 to 4:1 and having a density of above 0.8 kg/l @ 15° C.

[0018] The composition may have a viscosity below 4.1 cSt.

[0019] The volumetric blending ratio may be from 1:4 to 4:1.

[0020] The volumetric blending ratio may be from 1:2 to 2:1.

[0021] Typically the volumetric blending ratio is 1:1.

[0022] The hydrocarbon composition may have a cetane number in excess of50 typically in excess of 55.

[0023] The hydrocarbon composition may have a Cold Filter Plugging Point(CFPP) in accordance with IP 309 of below −12° C., typically below −15°C.

[0024] Typically the biodiesel may comprise of a mixture of linearC₁₀-C₂₀ methyl esters with minor quantities of water, glycerol andmethanol.

[0025] The Fischer-Tropsch hydrocarbon which is blended with biodieselmay be derived from a Fischer-Tropsch synthesis process using a catalystwhich is based on a metal selected from a group consisting of iron,cobalt or ruthenium or mixtures thereof.

[0026] The composition of the Fischer-Tropsch hydrocarbon may include avarying mixture of paraffins, olefins and oxygenates. Typically theFischer-Tropsch hydrocarbon comprises a mixture of both linear andbranched C₈-C₂₀ paraffins, C₉-C₂₀ olefins and C₇-C₂₀ alcohols.

[0027] The Fischer-Tropsch hydrocarbon may be a Fischer-Tropsch diesel.

[0028] The Fischer-Tropsch hydrocarbon preferably includeshydroprocessed Fischer-Tropsch hydrocarbon.

[0029] The invention extends to a blending component for a hydrocarboncomposition useful in Compression Ignition engines (CI engines), saidblending component comprising a blend of Fischer-Tropsch derivedhydrocarbon and biodiesel in a volumetric ratio of from 1:5 to 4:1.

[0030] The blending component may have a density of at least 0.8 kg/l at15° C.

[0031] The blending component may have a viscosity below 4.1 cSt.

[0032] The volumetric blending ratio of Fischer-Tropsch derivedhydrocarbon and biodiesel in the blending component may be from 1:4 to4:1.

[0033] The volumetric blending ratio of Fischer-Tropsch derivedhydrocarbon and biodiesel in the blending component may be from 1:2 to2:1.

[0034] Typically the volumetric blending ratio of Fischer-Tropschderived hydrocarbon and biodiesel in the blending component is 1:1.

[0035] The invention extends to a method of increasing the density of ahydrocarbon fuel composition having a density of below 0.8 kg/l to above0.8 kg/l, said method including blending of biodiesel into the fuelcomposition in a volumetric ratio of bio-diesel to hydrocarbon fuelcomposition of at least 1:3 as calculated before the blending in of thebio-diesel, thereby to obtain a resulting fuel composition having adensity of above the 0.8 kg/l threshold.

[0036] The volumetric ratio may be at least 1:2, typically about 1:1.

EXAMPLE OF THE INVENTION

[0037] The invention will now be illustrated, without limiting the scopethereof, by way of the following examples and illustrative values.

Example 1 Blending Rapeseed Methyl Ester with HydroprocessedFischer-Tropsch Derived Diesel

[0038] A hydroprocessed Fischer-Tropsch derived diesel, also referred toas a gas-to-liquids or GTL diesel, was blended in various volumetricratio's with rapeseed methyl ester and the properties thereof weremeasured.

[0039] Blending Gas-to-Liquid (GTL) Fuel, a hydroprocessedFischer-Tropsch derived diesel, with biodiesel has synergistic benefitswhich are obtained from the combined good qualities of both fuels.Neither biodiesel nor GTL Fuel contains aromatics or sulphur, whichwould normally limit blending ratios with conventional diesel. GTL Fuelimproves the cold flow properties and increases the viscosity associatedwith biodiesel. On the other hand, Biodiesel increases the GTL Fueldensity without weakening its low energy density. More biodiesel (50%)can be mixed with GTL Fuel when used as a replacement base fuel than thestandard 20% blends with conventional diesel.

[0040] Biodiesel is prone to gel formation in cold weather. GTL Fuel, onthe other hand, has good cold flow properties and a high cetane value asa consequence of the predominately methyl branching that occurs in theterminal positions of the paraffinic chains during the isomerisationprocess. This type of branching prevents wax crystallisation whilemaintaining a high cetane number. GTL Fuel has excellent thermalstability that exceeds premium diesel requirements. Other good biodieselproperties include its high flash point, which makes it a safe fuel touse. Both GTL Fuel and Biodiesel are readily biodegradable and non-toxicif spilt.

[0041] GTL Fuel—Biodiesel blends were prepared from biodiesel that wasproduced from rapeseed oil, (also called rapeseed methyl ester). Theblend formulations comprised 90%, 80%, 65%, 50% and 20% biodieselmixtures with GTL Fuel. The fuel properties of GTL Fuel and biodieseland blends thereof, are shown in Table 1, 2 and Table 3. The digitsfollowing the B in the table header indicate the volumetric percentageof the biodiesel in the composition.

[0042] The net, or lower, volumetric heating values of the GTLFuel—biodiesel blends (see Table 2) were calculated from the grossheating value results obtained through the ASTM D240 test method, bysubtracting the heat of condensation of water. TABLE 1 Fullspecification analysis of GTL Fuel - biodiesel blends Analysis UnitsMethod B100 B90 B80 B65 B50 B20 GTL Colour ASTM 1 1 1 1 1 <1 <1 D1500Appearance Caltex 1 1 1 1 1 1 1 CMM76 Density @ 20° C. kg/l ASTM 0.8800.868 0.857 0.839 0.822 0.788 0.764 D4052 Density @ kg/l ASTM 0.8830.871 0.860 0.843 0.825 0.791 0.768 15° C. D4052 Distillation ASTM D86IBP ° C. 323 173 166 166 162 153 150  5% ° C. 333 186 228 199 189 176173 10% ° C. 335 321 285 222 204 185 178 20% ° C. 336 330 320 280 239203 192 30% ° C. 337 333 330 312 278 225 208 40% ° C. 337 335 334 326306 249 226 50% ° C. 338 336 336 332 321 271 244 60% ° C. 338 337 338335 330 294 263 70% ° C. 339 338 339 337 334 310 281 80% ° C. 341 339340 339 337 323 297 90% ° C. 346 342 343 342 340 333 315 95% ° C. 352353 355 352 348 338 326 FBP ° C. 354 359 360 357 355 345 334 Recoveryvol % 99 99 98 99 99 99 98 Residue vol % 0.5 0.5 1.0 0.5 0.5 0.7 1.0Flash point ° C. ASTM D93 125 100 84 73 68 61 59 Viscosity cSt ASTM 4.494.11 3.72 3.28 2.89 2.27 1.97 @40° C. D445 CFPP ° C. IP 309 −12 −13 −14<−15 <−15 <−15 −20 Ash content mass % ASTM <0.01 <0.01 <0.01 <0.01 <0.01<0.01 <0.01 D482 Sediment mass % ASTM <0.01 <0.01 <0.01 <0.01 <0.01<0.01 <0.01 D473 Water vol % ASTM 0.033 0.023 0.022 0.019 0.015 0.0080.003 D1744 Carbon mass % ASTM 0.19 0.17 0.14 0.11 0.08 0.03 0.02Residue D524 Sulphur mass % ASTM 0.0004 0.0004 0.0003 0.0003 0.00020.0001 0.0001 D5453 Cu corr. rating ASTM 1b 1b 1b 1b 1b 1b 1b D130 Acidnumber mgKOH/g ASTM 0.101 0.086 0.073 0.056 0.048 0.023 0.001 D664Cetane ASTM 63 63 63 63 66 69 71 D613 Elec. pS/m 140 130 100 70 40 10 0Conductivity O₂ stability mg/100 ml ASTM 5.7 4.8 4.1 3.1 2.1 0.16 0.21D2274 Bromine gBr/100 g IP 129 77.1 68.4 59.3 53.2 38.0 15.9 0.8 numberNitrogen mg/l ASTM 2 1 1 1 1 <1 <1 D5291

[0043] TABLE 2 Heat of combustion of GTL Fuel - biodiesel blends GrossHydrogen Net heating heating value content value Density Net heating(MJ/kg) (mass %) (MJ/kg) (kg/l) value (MJ/l) B(100) 39.973 11.92 37.4440.880 32.950 B(90) 40.565 12.15 37.987 0.868 32.973 B(80) 41.330 12.8138.612 0.857 33.090 B(65) 42.124 13.69 39.219 0.839 32.905 B(50) 43.18913.19 40.390 0.822 33.201 B(20) 45.346 14.42 42.286 0.788 33.321 GTL47.015 14.98 43.836 0.764 33.491

[0044] The lubricity properties of the GTL Fuel—biodiesel blends weredetermined according to the ASTM D6078 and ASTM D6079 test methods whichdefine the scuffing load ball-on-cylinder (SL BOCLE) and high-frequencyreciprocating rig (HFRR) lubricity evaluation test methods respectively.Results are shown in Table 3. TABLE 3 High-frequency reciprocating rig(HFRR) and scuffing load ball-on-cylinder (SL BOCLE) lubricityevaluation of GTL Fuel - biodiesel blends B100 B90 B80 B65 B50 B20 GTLHFRR 141 156 150 148 152 166 651 (WSD μm)SL >6000 >6000 >6000 >6000 >6000 6000 2800 BOCLE Load g

[0045] Characterisation and quantification of the neat biodiesel and GTLFuel was obtained through Gas Chromatograph Mass Spectrometry (GC MS),Gas Chromatograph Flame Ionisabon Detection (GC-FID) and FluorescentIndicator Adsorption (FIA).

[0046] Diesel density specifications are tending to become tighter. Thisis due to the conflicting requirements of a lower density fuel to reduceparticulate matter emissions, whilst retaining a minimum density toensure adequate heat content, which relates to fuel economy. Thetightening density specification can be seen from the EN 590:1999 DieselFuel Specifications which correlates to EURO 3 emission specifications.Since biodiesel has a higher density than GTL diesel, the greater thebiodiesel fraction in the biodiesel—GTL Fuel blends the higher itsdensity (see Table 1 and Table 2). A blend including 30% biodieselexceeded a density of 0.8 kg/l

[0047] In general, the higher the density of a hydrocarbon fuel, thegreater is its volumetric heat of combustion and the lower is itsvolumetric fuel consumption. However, from Table 2 it is obvious thatbiodiesel, which is not a hydrocarbon fuel but a methyl ester, has a lownet volumetric heating value, also called energy density. Biodiesel willtherefore not assist in raising GTL Fuel's energy density but will notlower it significantly. In terms of specifications, higher density forGTL Fuel can therefore be realised by biodiesel blending withoutinfluencing its energy density negatively.

[0048] Distillation temperature also influences emissions. A high T90 orT95 temperature will increase the quantity of unburned hydrocarbons andthe level of particulate matter emitted. All GTL Fuel—biodiesel blendformulations were below the maximum current T95 distillation EN 590Diesel Specification limit of 360° C.

[0049] GTL Fuel is mostly paraffinic in nature. 98% (volume %) GTL Fuelis comprised of paraffins and 2% comprises olefins in a hydrocarbonrange from C8 to C24. Less than 0.001 volume % aromatics are present inGTL Fuel according to FIA analysis.

[0050] In an engine, the viscosity influences the injection fuel spray.Fuel with a very high viscosity can reduce fuel flow rates, resulting ininadequate fuelling. Such a fuel also atomises poorly, resulting in poorcombustion, loss of efficiency and an increase in CO and hydrocarbonemissions. On the other hand, if the fuel viscosity is too low, theinjection spray is too soft and will not penetrate far enough into thecylinder and loss of power will occur. Blending GTL Fuel with biodieselimproves the CFPP value of biodiesel and it is possible to attain thewinter grade specifications of some European countries (see Table 1).

[0051] Like GTL Fuel, neat rapeseed methyl ester (RME), or biodiesel,has a high cetane number relative to conventional diesel. Blends ofbiodiesel with GTL Fuel exhibit a high cetane number.

[0052] GTL Fuel blends with biodiesel also improves fuel properties thatdo not affect engine performance directly. These include the high watercontent, acid number, bromine number, oxygen stability of biodiesel andthe tendency of biodiesel to form carbonous residue. The amount of waterpresent in the neat biodiesel and its acid number are within the EUDraft Specification for biodiesel and ASTM PS121 biodieselspecifications, but is much higher than conventional or synthetic dieselfuel and can lead to corrosion problems. Biodiesel blend formulationswith GTL Fuel, with its very low water content and acid number, decreasethe water content and acid number of biodiesel proportionally.

[0053] The bromine number of GTL Fuel is very low because it containsless than 2% olefins whereas that of biodiesel is high (see Table 1)because of the large percentage unsaturated methyl esters. Blending ofGTL Fuel with biodiesel does not only decrease the susceptibility ofbiodiesel to gum formation by lowering the bromine number, but alsoincreases biodiesel's resistance to degrade in the presence of oxygen.The insolubles formed in neat RME in the presence of oxygen is muchhigher than specified according to the Biodiesel EU Draft Specification.

[0054] Thus, it is believed, more biodiesel can be mixed with GTL Fuelthan the standard 20% blends with conventional diesel. GTLFuel—biodiesel blend ratios up to 50% biodiesel still comply withpresent EN 590:1999 Diesel Specifications. This is in part due to thehigh cetane number, good cold flow properties and stability of GTL Fuel.Neither biodiesel nor GTL Fuel contains aromatics and both are sulphurfree. GTL Fuel improves the cold flow characteristics of biodiesel,whereas biodiesel does not negatively effect the energy density of theGTL fuel.

[0055] Biodiesel increases GTL Fuel density without influencing the GTLFuel energy density negatively.

[0056] The inventors further believe that advantage of the inventioninclude that with progressively increased blending, the biodieselcharacteristics are improved with respect to:

[0057] cetane number exceeds recommended 55

[0058] density is reduced to within the desired range

[0059] viscosity is reduced to within the specified range

[0060] the overall calorific value is closer to “standard” ULSD diesel

[0061] the flash point is closer to “standard” ULSD diesel

[0062] the cold flow properties are better

[0063] the T90 distillation is moderated slightly downwards

[0064] It is believed that positive biodiesel characteristics such asthe low aromatics and sulfur content and biodegradability are retained.

[0065] The GTL fuel—biodiesel blend may be utilised as a blendingcomponent for blending with crude derived diesel without adverselyaffecting the good GTL properties or on-spec crude derived qualities.

[0066] Thus, blending Fischer-Tropsch hydrocarbons with biodiesel allowsa more compatible mixture and high biodiesel content, whereas blendingbiodiesel with crude based diesel favours predominantly a minor fraction(520%) of diesel.

[0067] The Fischer-Tropsch hydrocarbon-biodiesel blend may be used as ablending component for blending with crude derived diesel in any blendratio to enhance the crude derived diesel quality without adverselyaffecting any of the properties typically included in specifications forcrude derived diesel.

1. A hydrocarbon composition for use in compression ignition engines(CI), said composition comprising a blend of Fischer-Tropsch derivedhydrocarbon which includes hydroprocessed Fischer-Tropsch hydrocarbon,send blend having a density of below 0.8 kg/l at 15° C. and bio-dieselhaving a density of above 0.8 kg/l at 15° C. in a volumetric ratio offrom 1:4 to 4:1, said composition having a density of above 0.8 kg/l at15° C. while maintaining the Fischer-Tropsch derived hydrocarbon's netvolumetric heating valve.
 2. A hydrocarbon composition as claimed inclaim 1, having a viscosity of below 4.1 cSt.
 3. A hydrocarboncomposition as claimed in claim 1, wherein the volumetric ratio is from1:2 to 2:1.
 4. A hydrocarbon composition as claimed in claim 3, whereinthe volumetric blending ratio is 1:1.
 5. A hydrocarbon composition asclaimed in claim 1, having a cetane number in excess of
 50. 6. Ahydrocarbon composition as claimed in claim 5, having a cetane number inexcess of
 55. 7. A hydrocarbon composition as claimed in claim 1, havinga CFPP in accordance with IP 309 of below −12° C.
 8. A hydrocarboncomposition as claimed in claim 7, having a CFPP in accordance with IP309 of below −15° C.
 9. A hydrocarbon composition as claimed in claim 8,wherein the biodiesel comprises of a mixture of linear C₁₀-C₂₀ methylesters with minor quantities of water, glycerol, and methanol.
 10. Ahydrocarbon composition as claimed in claim 1, wherein theFischer-Tropsch hydrocarbon which is blended with bio-diesel is derivedfrom a Fischer-Tropsch synthesis process using a catalyst which is basedon a metal selected from a group consisting of iron, cobalt, andruthenium, or mixtures of two or more thereof.
 11. A hydrocarboncomposition as claimed in claim 1, wherein the composition of theFischer-Tropsch hydrocarbon includes a mixture of paraffins, olefins,and oxygenates.
 12. A hydrocarbon composition as claimed in claim 11,wherein the Fischer-Tropsch hydrocarbon comprises a mixture of bothlinear and branched C₉-C₂₀ paraffins, C₉-C₂₀ olefins, and C₇-C₂₀alcohols.
 13. A hydrocarbon composition as claimed in claim 1, whereinthe Fischer-Tropsch hydrocarbon is a Fischer-Tropsch diesel. 14.(Canceled)
 15. A blending component as claimed in claim 14, having adensity of at least 0.8 kg/l at 15° C.
 16. A blending component asclaimed in claim 14, having a viscosity below 4.1 cSt.
 17. A blendingcomponent as claimed in claim 14, wherein the volumetric blending ratioof Fischer-Tropsch derived hydrocarbon and biodiesel in the blendingcomponent is from 1:4 to 4:1.
 18. A blending component as claimed inclaim 14, wherein the volumetric blending ratio of Fischer-Tropschderived hydrocarbon and biodiesel in the blending component is from 1:2to 2:1.
 19. A blending component as claimed in claim 14, wherein thevolumetric blending ratio of Fischer-Tropsch derived hydrocarbon andbiodiesel in the blending component is 1:1.
 20. A method of increasingthe density of a hydrocarbon fuel composition having a densisty of below0.8 kg/l to above 0.8 kg/l, said method including blending of bio-dieselinto the fuel composition in a volumetric ratio of bio-diesel tohydrocarbon fuel composition of at least 1:3 as calculated before theblending in of the bio-diesel, thereby to obtain a resulting fuelcomposition having a density of above the 0.8 kg/l threshold and a netvolumetric heating value of about 33 000 MJ/m³ wherein said fuelcomposition includes hydroprocessed Fischer-Tropsch hydrocarbon.
 21. Amethod as claimed in claim 20, wherein the volumetric ratio is at least1:2.
 22. A method as claimed in claim 21, wherein the volumetric ratiois about 1:1.
 23. (Canceled)